1. Field of the Invention
The present invention relates to an interrupt control apparatus, a bus bridge, a bus switch, an image processing apparatus and an interrupt control method in a system such as PCI-Express (to be referred to as “PCIe” hereinafter) in which interrupt notification is performed by packet transfer or by edge interrupt.
2. Description of the Related Art
As a conventional technique, a technique is proposed for reducing a number of terminals by sharing interrupt input lines in a device having a plurality of PCI buses (refer to Japanese Laid-Open Patent Application No. 2005-092770, for example). In addition, a technique is proposed in which an interrupt control unit selects an interrupt when transmitting it to an upper device, and invalidates and discards input and output interrupt packets under resetting (refer to Japanese Laid-Open Patent Application No. 10-149293, for example).
In the following, an interrupt control method of the PCIe bus is described. The PCIe bus does not have a specific interrupt signal, and requests an interrupt using a packet. The packet for interrupt is called a MSI (Message Signaled Interrupt) packet. Interrupt factors can be classified to 32 types at the maximum using a message number that is embedded in the MSI packet so that 32 types of interrupt factors can be notified at the maximum.
A number of message numbers (number of MSI messages) that can be embedded in MSI packets is set by a PCIe configuration cycle when the system is launched. In the PCIe standard, there are six kinds of the number of MSI messages, which are 32, 16, 8, 4, 2 and 1. The system determines which is to be selected. For example, when “number of MSI messages=32” is selected, a device that can transmit MSI packets using 32 MSI message numbers can transmit a MSI packet embedding a message number that is any one of 32 kinds of numbers (0-31).
In addition, when “number of MSI messages=16” is selected, the device that can transmit MSI packets using 32 MSI message numbers assigns a same message number to two factors to transmit a MSI packet. When “number of MSI messages=8” is selected, a device that can transmit MSI packets using 32 MSI message numbers assigns a same message number to four factors to transmit a MSI packet.
When “number of MSI messages=4” is selected, a device that can transmit MSI packets using 32 MSI message numbers assigns a same message number to eight factors to transmit a MSI packet. When “number of MSI messages=2” is selected, a device that can transmit MSI packets using 32 MSI message numbers assigns a same message number to 16 factors to transmit a MSI packet. In addition, when “number of MSI messages=1” is selected, a device that can transmit MSI packets using 32 MSI message numbers assigns a same message number to all (32) factors to transmit a MSI packet.
However, according to the interrupt control method of the PCIe bus of the above-mentioned conventional technique, when 16, 8, 4, 2 or 1 is selected as the number of MSI message numbers, a same message number is assigned to a plurality of interrupt factors. When a MSI packet in which a same message number is embedded is issued a number of times, there is a problem in that traffic of the PCIe bus increases so that performance of the device may be lowered.